Butadiene emulsion polymerization process, including mercaptan and cyanide modifiers



PetentedJune 14.1w

BUTADIENE EMULSION POLYMEBIZATION PROCESS, INCLUDING MEBCAPTAH ANDOYANIDE MODIFIERS Hamid J. Rose and m Kabler Rowan, Baton Rouge, La.,assignorl to Standard Oil Development Company, a corporation of DelawareNo Drawing. Application August so, 1944. Serial No. 551.424

4 Claims. (Cl. 260-845) This invention pertains to the production ofsynthetic rubber-like materials by the polymerization of certainunsaturated materialsin aqueous emulsion.

Synthetic rubber-like materials have been prepared ior some time bypolymerizing conjugated diolefln hydrocarbons of 4 to 6 carbon atoms.such as butadiene-1,3. isoprene, dimethylbutadiene and the like, singlyor in combination or in admixture with compounds containing a single C=Clinkage and capable of copolymerizing'with diolefln. hydrocarbons inaqueous emulsion.

Such copolymerizable compounds have included portions in which they areused and the reaction I conditions applied. As a rule, the soft rubberypolymers result when the diolefln is the preponderant polymerizablematerial; provided, of course, that other reaction conditions are right.A major problem in the preparation of emulsion polymers has been that ofspeeding up the rate of reaction. While numerous materials or expedientsmay be applied in order to increase the reaction rate, the bulk of themare objectionable since they injure product quality. For example, therate of reaction may be increased byusing an optimum catalystconcentration or by raising the-temperature at which the reaction isconducted. The polymer obtained in either of these ways is not assatisfactory as that obtainable at lower temperatures or in the presenceof smaller amounts of catalyst. The most satisfactory polymerizationmodifiers that have been found to date are aliphatic mercaptanscontaining more than six and preferably about twelve carbon atoms permolecule, as disclosed in U. 8.

Patent No. 2,281,613. Although the use of these mercaptans serves topromote or increase the speed of the reaction, there is still a demandthat the reaction be further speeded up.

It is the object of this invention to provide the art with a novelmethod of activating emulsion polymerization reactions.

It is also the object of this invention to activate the emulsionpolymerization of dioleflns or of mixtures of dioleflns withcopolymerizable com-' pounds without detrimentally ailectlng the polymerproduct quality.

It is a further object of this invention to actlvate the emulsionpolymerization reaction in order to form polymers of good quality at thetemperatures usually applied in a shorter time.

It is also the object of this invention to activate the emulsionpolymerization reaction in order to form polymers of better quality atlower tempera tures in the same or in somewhat shorter time thanordinarily allowed.

These and other objects will appear more clearly from the detailedspecification and claims which follow.

We have now found that the production of synthetic rubber-like materialsby the emulsion polymerization of dioleflns or mixtures of dioleflnswith copolymerizabie materials occurs at a much faster rate and/or atlower temperatures without injury to the product quality if small andcritical amounts of a water-soluble cyanide such as sodium or potassiumcyanide or other soluble salt oi hydrocyanic acid is provided in thereacticn mixture. The cyanide is preferably added to the reactionmixture as a freshly prepared solution after all other ingredients havebeen addw.

The activating effect of small amounts of'soluble cyanides is "quitesurprising since larger amounts have been used in polymerization recipesand apparently exercised a poisoning effect upon the polymerization.Such a recipe is disclos in an article by Mueller in India Rubber World,volume 107, October, 1942, pages 33-35. Several runs were made using thefollowing recipe with check runs on each in which the potassium cyanidewas omitted. The recipe used was as follows:

Grams per pressure bottle 7 Reactants Parts charge Butadiene 100. 50100. 2 8; P0 1211 0) 8 4. 0. 5 1.09 gitric acid. H 0). q l. 5 3.0.Potassium cyanide" 0.1 0.2. Carbon tetrachloride. l. 5 3.0.

Sodium Perborate.. 0. 075 0% (N aBOMH O). Acotaldeliyde 0.3 0.6.

The data obtained using the recipe shown above are not in accord withthe 3-5 hour reaction time at room temperature as reported in Mueller'sarticle. In addition, the reaction proceeded at a faster rate in theabsence of iron than it did when KC'N was used in the concentrationrecorded above. Data from two sets bottle experiments are shown below:

Per Cent xoN ln' Cent Conver Time aaaanmae-n as butadiene, isoprene,piperylene, dimethyl-butadiene or the like. used singly or mixtures-oisuch dioleiins, as well as mixtures oi conjugated dioleflns, such asbutadiene or isoprene, with copohrmerizable materials containing a,single C=O linkage such as styrene, alpha-methyl-styrene.para-methyl-styrene, alpha-methyl, para-methyl styrene,para-chloro-styrene. acrylonitrile, methaerylonitrile,chioroacrylonitrile, acrylic acid esters such as methyl acrylate ormethyl methacrylate and unsaturated ketones such as methyl vinyl ketoneand the like.

The polymerization is ordinarily eiiected by disone and one-half to twoparts oi water containing a suitable emulsifying agent, polymerization.

catalyst and mercaptan polymerization modifier.

The emulsifiers employed are the alkali metal or ammonium salts orhigher molecular weight iatty acids such as oleic acid, stearic acid,Distal acids and the like. alkali metal salts of alkylated sulfonicacids or fatty alcohol sulfates, for example, sodium salts of isobutylnaphthalene sulionic acid. tetraisobutenyl sulionic acid and also acidaddition salts of high molecular amines such as dodecyl aminehydrochloride or acetate and the like. The amount of emulsifier used isordinarily about 0.5 to about 5 weight per-cent based on the monomers.

The catalysts which may be used in the polymerization are substanceswhich are capable of liberating oxygen under the conditions employed inthe polymerization and include such compounds as hydrogen peroxide,benzoyl peroxide, alkali metal or ammonium perborates and persulfates,or the like. The amount of catalyst is ordinarily about 0.05 to about0.6 weight per cent based upon the monomers present.

The polymerization modifiers provided in our reaction mixture are thehigher molecular aliphatic mercaptans, i. e., containing more than aboutsix carbon atoms per molecule, such as octyl, dodecyl and "Lorol"mercaptan. Lorol mercaptan is a mixture of mercaptans consisting oiapproximately 55% of Cu, 30% of Cu and of C16 mercaptans. Tertiarymercaptans such as diisobutyl mercaptan, or aromatic mercaptans, mayalso be used. The amount of modifier used is ordinarily about 0.2 toabout 1.0 weight per cent based upon the monomers used.

The cyanides that may be used to activate the emulsion polymerizationreaction in accordance persing one part oi the monomers in from about Iwith the present invention are sodium or potassium cyanide or any otherwater-soluble salts oi hydrocyanic acid such as ammonium. calci-- um,barium or magnesium cyanide. 'lhe amount 01' activator used is verysmall, varying between about 0.0008 and about 0.02 weight percent of thecyanide ion based upon the monomers.

The following examples are illustrative of the present invention but itis to be understood that our invention is not limited thereto:

A eopolymer or butadlene and acrylonitrile was prepared in a King #1syphonbottleaccord- 1118 to the following recipe:

Parts 0.3 or as given 015 2 0. or as given 1.

and mercaptan were added to the emulsion. At this point butadiene wasintroduced to the bot-- tie reactor. The bottle was then placed in awater bath where it, was subjected to tumbling type agitation for therecorded periods or time. The temperature was maintained at F. exceptwhere otherwise stated.

The foregoing experiment was repeated several times using identicalmaterials except that varying sniall amounts of a freshly prepared0.016% cyanide (equivalent to 0.04% KCN) solution were added to thereaction mixture just beiore the butadiene was charged.

Another series of -similar experiments was conducted using constantamounts of cyanide and catalyst and varying amounts of mercaptan.

In addition, another series of experiments was carried out usingconstant amounts of cyanide and mercaptan and varying amounts oi.catalyst.

The polymer produced in each of these runs was separated by coagulatingthe'latex obtained with saturated brine and adjusting the particlePolymer Zinc oxide Stearic acid Benzothiazyl disulflde Sulfur 1.5

Medium processing Channel Black 50 The resulting vulcanlzates were thenevaluated. The data obtained are summarized in Tables Lnandm.

Parts Teen: I Cyanide activated synthesis of butadiene-acrvlo ni'trllepolymers variable cyanide concentration Williams Mcr- Conver- ReactionConvex 3007 Plast. Bun KON .K;8 on Time slgg l er Tensile Elong. Modufus Mmb cated Per Cent Per Cent Per Cent Per Cent Per Cent Per Cent31-7 0 0. 66 0. 8 63. 0 13. 26 4. 7 133-32 0. 006 0. 66 0. 8 70. 6 7. 9.7 4, 600 626 1, 125 100-10 0.01 0. 66 0.8 67. 6 6. 26 10. 8 4, 650 1,300 117-12 0. 016 0. 66 0. 8 69. 5 8. 75 7. 9 4, 150 510 1, 600 145-680.02 0.66 0.3 78. 6 12. 6.3 4, 460 1, 950 149-79 TABLE II Cyanideactivated synthesis of butadiene-acrulonttrtle polymers variablemercaptan concentration Mer- Conver- Reaction Conver' 300% Bun KONK1810: on Time slgrguprer 'lenslle Elong. Modulus Mastp cated Per CentPer Cent Per Cent Per Cent Per Cent Per Cent 0. 006 '0. 8 0. 3 62. 0 8.07. 8 4, 450 490 1, 850 -11 0. 006 0. 4 0. 3 69. 6 7. 6 7. 9 4, 300 5301, 500 132-14 0. 006 0. 5 0. 3 67. 0 7. 0 9. 6 4, 600 670 1, 375 108-100.006 0. 6 0. 3 62. 0 7. 0 8. 9 4, 660 690 1, 450 120-10 0. one 0. 7 0.3 62. 0 7. 6 8. 3 4, 650 610 1, 126-14 0. 005 0. 9 0. 3 66. 0 8. 0 8. 83, 700 680 1, 176 114-17 TABLE III Cyanide activated synthesis ofbutadiene-acrylonltrile polymers variable catalyst concentrationWilliams Reno. Time Conv. 3007 Plast. Run No. RON 1181! 0st. Convcr.(H158 per KL Tensile Elong. Modulus M asti cated Percent Percent PercentPercent Percent Percent BE-19-1..-.- 0 0. 6 0. 1 1 63. 6 15. 75 (92) 3.4 3, 850 680 925 71-4 0. 005 0. 6 0. 06 1 51. 0 8. 5 95) 6. 0 3, 900 5901, 100 82-2 0. M6 0. 6 0. 16 1 69.0 7. 25 95) 9. 5 3, 800 590 1, 02594-7 0W5 0.6 0.3) 71.0 9.00 95) 7.9 4, 160 490 1, 675 131-17 0.1!)6 0.60.40 71.6 10.60 96) 6.8 4,050 465 1,850 148-40 0.0)6 0. 6 0. G] 75. 510. 50 95) 7. 2 4, 200 445 2, 100 153-52 0.006 0.6 0.!) 77.0 12.00 95)6.4 4,100 400 2,500 173-77 0.006 0.6 1.00 78.0 12.00 95) 6.6 4,025 3902,650 179-94 Consldereble was observed in these experiments and some orthe reactions were consequently terminated at lower conversions an wasdesired. The formation of the viscous soap-like gel probably would notoccur it better owed-on were possible (or the bottle reactors.

7 It may readily be seen from the foregoing data that the concentrationsor cyanide are quite critical. It is rather diiiicult, howeven, to limitthe concentrations to a very narrow range since a they are dependent toa certain degree .on the concentrations of both mercaptan and catalystand indirectly to the purity of the raw materials since the latter varcentration available for the actual mlymerization reaction.

EXAMPLE 2 Butadiene-acrylonitrile eopolymers were prepared at atemperature of 76 F. both with and without cyanide activation. Thepolymerization recipe, charging procedure, etc., were-identical theeil'ective catalyst con-' with those described in. Example 1. The dataobtained are summarized id'rebie IV:

. 8 oxide. Ai'terbeingthoroughly waahadthecrumb polymer was reslurriedin warm water several times to remove soap and brine, after which it wasdropped on to the fliten'and dried at 180 1".

for approximately 18 hours. The conversion was determined by weighingthe dry polymer obtained from aglven weight of latex and compar- ,5;Ocnver. g;; The '-,;'gg ass. as?

Pemat Percent Percent Percent Phrasal I Percent 41 .45 11.1) as 4,200are m a an no u 4,oo o s50 l e-n it 32 ti tit it? 23 $2 on no so asoo mo000 73-0 These runs show thatsmall amounts oi cyanide Parts activatesthe copolymerization of butadiene- Polym r acrylonitrile at lowertemperatures, giving a, con- Zinc oxide version rate of about4.95.4%/hr. as compared Stearic acid 1.5 to 2.7-2.8%/hr. withoutactivation. It also ap-- 35 Sulfur pears that the activation is eiiectedwithout siib- Benzothiaayl disulijide 1.25 stantialiy aiiecting thephysical properties of the Diphenyl guanidine 0.26 polymer. 7 Mediumprocessing Channel Black. m 3 C081 tar type softener 4 40 Wood rosin 4Butadiene-acrylonitrile copolymers were also Ozokerite, 15

prepared in a series of pilot plant runs made in a fifty gallon reactorprovided with turbo type agitation. The recipe used was as follows:

Butadiene '14 Acrylonitrile 26 Water v 200 Oleic acid 5 Sodium hydroxide(to neutralize 73% 01' oleic acid) Potassium persulfate 0.6 Lorolmercaptan 0.48

Total reactants charged80 lb,

cept where specified) and the reaction allowed to proceed.

After the reaction proceeded to approximately I 70% conversion, thecharge was taken. from the reactor to the stripper where it wasstabilized with 2% phenyl beta-naphthylamine and the unused reactantswere removed by raising the-- temperature somewhat and passing steamthrough the latex for a given length of time during which it was keptunder vacuum. After being stripped, the latex was pmed to the coagulatorwhere it was coagulated with saturated brine and the particle size wasadjusted with carbon di- The vuicanizates so obtained were evaluated andthe data obtained are summarized in Table V.

Tana: V I

Synthesis of butadiene-acrylonitflle polymers pilot plant operationusing cyanide activated system v 0% KCN and 0.58% BSH.

EXAMPLEL A copolymer oi butadiene and styrene was prepared usingpressure bottles (King No. 1 siphon bottles), agitated by rotation on awheel in a water bath in the usual manner. All the runs were made withthe following-recipe unless otherwise stated; the parts given are byweight:

. Parts Butadiene 75 Styrene 25 Water 200 Sodium soap of selectivelyhydrogenated Distal acid 5 Potassium persulIate-...- 0.3

All runs were made at 40 C. for 16 hours and using 200 grams ofreactants. when potassium cyanide was used, it was added as a freshlyprepared 0.5% solution and mixed well into the emulsion just prior tothe addition of the mercaptan and butadiene. The polymer was separated,dried, compounded and evaluated substantially as described in Example 1.The data obtained are summarized in Table VI below:

' Trista VI KCN as promoter for Buna S Synthesis It may be observed thatabove about 0.016% of KCN no acceleration of reaction rate occurs andthat there is a maximum conversion obtainable over a range of about0.002% of KCN. It is obvious from these data that the operable is quitecritical.

Eutadiene-styrene copolymers were prepared using a selectivelyhydrogenated Distal acid soap oi. diflerent degrees of neutralization inorder to determine the eflect of alkali on the activation of thispolymerization by means of potassium cyanide. The following recipe wasused in the several runs: I

All of the runs were at 40 C. for 15 or 16 hours and using' 200 grams ofreactants. The results obtained are summarized in- Table VII.

Parts Butadiene 100 Water 200 Ivory soap 5 Potassium persuliate 0.8Lorol mercaptan 0.4

The temperature was maintained at 107 F. for the reaction time of 15hours. The results obtained are summarized in Table VIII below:

m: vm

Run KON 1 Convey. 33:75:. sion l l er Per cent Per cent Per cent 0.00 m5 o 005 32.0 a 5 0.010 92. 5 a 0. 015 89. 5 6 0 0. 020 85. 5 7

1 Percentage oi KCN is on hydrocarbon basis.

The increase in reaction rate obtained is of the same order of magnitudeas for the copolymerization of butadiene and acrylonitrile as well asfor the copolymerization of butadiene and styrene.

It may readily be seen from the foregoing exampies that small, criticalamounts of water soluble salts'of hydrocyanic acid exert a pro-= nouncedactivating eflect upon the emulsion polymerization of conjugateddiolefins and mixtures of conjugated diolefins with copolymerizablecompounds.

The foregoing description contains a limited number of embodiments ofthe present invention.- It will be understood, however, that theforegoing examples are merely illustrative of the present invention andthat the latter is not limited to the specific conditions describedsince numerous variations are possible without departing from the scopeof our invention as defined by the following claims.

What we claim and desire to secure by Letters Patent is:

1. The process of preparing rubber-like emulsion polymerizates whichcomprises emulsifying in water a mixture of a major proportion of aconjugated diolefin hydrocarbon of 4 to 6 carbon atoms and a minorproportion of an ethylenically unsaturated comonomercapable ofcopolymerizing with conjugated dioleflns in aqueous emul- Tasts VIINeutmlizationof Seieotivel E Reaction Conver- Mooney 300%Elongdrogenated Distal and y KON Time sion Viscosity Tens Modulus anionPercent Per Percent 0.00 10 (2)59 13 0.00s -16 09.5 42 2,410 m 680 0.00315 73 0.003 10 00 50 2,340 1,080 580 0.003 15 75 0.003 10 1e 07 2,040820 090 0.003 15. 70.5 0.000 15 77 00 2,700 880 040 0.003 15 81 Thesedata show that the use of a very slight excess of alkali in conjunctionwith potassium cyanide appears to be suflicient to give a furtherimprovement in. reaction rate.

EXAMPLE 6 0.2 to 1.0 weight percent based on the monomers Polymers ofbutadiene alone were prepared in 4 pressure bottle experiments similarto those carried out in the preceding examples. The recipe used in theseveral runs were as follows:

of an aliphatic mercapta-n polymerization modifier containing 6 to 16carbon atoms per molecule,

and adding thereto 0.005 weight percent based on the monomers of cyanideion in the form of a water soluble salt of hydrocyanic acid.

' 2. A process according toclaim 1 wherein the emulsifier comprises afatty acid soap and up to 15 percent more alkali than is necessary forcomplete neutralization of the fatty acid in the soap, and wherein theethylenically unsaturated comonomer is styrene. v

3. A process according to claim i wherein the ethylenically unsaturatedcomonomer is styrene.

4. The process of preparing rubber-like emulsion polymerizates whichcomprises emulsifying one part of a'mixture'of a major proportion ofbutadiene-l,3 and a minor proportion of acrylonitriie in 1% to 2 partsof water in the presence of 0.5 to 5.0 weight percent based on themonomers of an alkali soap of a fatty acid, 0.05 to 0.6

' weight percent based on the monomers of an l2 anrnanncss orrnn Thefollowing references are of record in the file of this patent: 4

. UNITED STATE PATENTS Number Name Date 2,248.10! Meisenburg July 8,1941 2,281,813 Woilthan May 5, 1942 2,300,056 Mels oct. 27, 1943 8 ,735Borders Oct. 9, 1940 Number Country Date 550,280 Great Britain -m---Jan. 1, 1943 OTHER. REFERENCES Mueller, India Rubber World, pp. 3345 and41 (1942) Powers, Synthetic Resins a Rubbers (1948).

pp. ans-209. (Copy in Division to.)

